This invention is directed to an improved method for producing calcined coke agglomerates characterized by having good stability from caking, poorly caking and non-caking coals or blends of coals, char and optionally topped tar.
Reserves of good caking coals suitable for producing metallurgical grade coke are being depleted. Vast reserves of non-caking and poorly-caking coals are, however, available in this country. These reserves of coals are generally not usable in producing metallurgical grade coke in slot-type coke ovens.
In recent years, processes utilizing the non-caking coals and poorly-caking coals have been developed. Several processes are directed to mixing the coal with a binder and briquetting coal under pressure at a desired temperature. The coal briquettes thus formed are then calcined to elevated temperatures in either a one step process or a multi-step process to produce coke briquettes.
Other processes in which coal is agglomerated by mixing it with char, a solid distillation residue remaining after low temperature carbonization of coal, and a binder in a rotating drum and heating the mixture while being tumbled have been proposed. The agglomerates formed by the tumbling action are charged while hot into a vertical furnace to be calcined at elevated temperatures to produce coke agglomerates.
Caking coals when heated to temperatures of about 750.degree. to 850.degree. F. (399.degree. to 454.degree. C.) become fluid, that is, they become soft and plastic. Volatiale material in the coals is driven off and the coals fuse or agglomerate. After a time the coals resolidify and relatively hard coal agglomerates are discharged from the drum. Non-caking or poorly-caking coals are difficult, if not impossible, to soften and plasticize at any temperature. As a result, these coals are not readily agglomerated. In order to agglomerate these coals it is necessary to add large quantities of a binder to the coals. Throughput of these coals to produce product sized agglomerates is low and hence production is low. Then, too, calcined coke agglomerates made from these coals generally have poor stability. Caking coals, on the other hand, may be so fluid that when they become fluid they adhere to and build up as a scale deposit on the wall of the rotating drum. It is frequently necessary to use a scraper in the drum to prevent or reduce the size of the deposition of the scale on the wall. Scale deposits can become so great that the drum must be taken out of service so that the material adhering to the wall can be removed. Greater quantities of char than normal must be added to the coals in the drum to reduce the tendency of the coals to adhere to the wall. As a result, throughput of coals is reduced, production is reduced, and the process becomes economically unfeasible.